Voice echo suppression in engine order cancellation systems

Abstract

Engine order cancellation (EOC) systems generate feed forward noise signals based on the engine or other rotating shaft RPM and use those signals and adaptively configured W-filters to reduce the in-cabin SPL by radiating anti-noise through speakers. An EOC system may include a signal analysis controller for detecting non-stationary events, such as speech, based on parameters sampled from a current frame of error signals output from microphones positioned in various locations of a vehicle passenger cabin. Upon detection, the signal analysis controller may mitigate the effects of the non-stationary event to prevent the EOC system from boosting noise or contributing to a speech-like post-echo in the passenger cabin. For example, if speech is detected in a frame, then the adaptation can be frozen for that frame. Alternatively, the signal analysis controller may adaptively subtract voice signals out of the error microphone signal.

What is claimed is: 
     
       1. A method for preventing mis-adaptation in a feed-forward engine order cancellation (EOC) system, the method comprising:
 adjusting an adaptive transfer characteristic based on a noise signal received from a noise signal generator, an error signal received from a microphone located in a cabin of a vehicle, and an adaptation parameter; 
 generating an anti-noise signal based in part on the adaptive transfer characteristic, the anti-noise signal to be radiated by a speaker as anti-noise within the cabin of the vehicle; 
 detecting a non-stationary event based on signal parameters sampled from a frame of the error signal; and 
 modifying the adaptation parameter for a duration of the frame in response to detecting the non-stationary event. 
 
     
     
       2. The method of  claim 1 , wherein detecting a non-stationary event based on signal parameters sampled from a frame of the error signal comprises:
 comparing at least one signal parameter of a current frame for the error signal to a threshold; and 
 detecting the non-stationary event when the at least one signal parameter exceeds the threshold. 
 
     
     
       3. The method of  claim 2 , wherein the signal parameter is one of a peak amplitude of the error signal sampled in the frame and an energy value of each frame. 
     
     
       4. The method of  claim 2 , wherein the threshold is a predetermined static threshold programmed for the EOC system. 
     
     
       5. The method of  claim 2 , wherein the threshold is a dynamic threshold computed from a statistical analysis of the at least one signal parameter in one or more preceding frames of the error signal. 
     
     
       6. The method of  claim 1 , wherein detecting a non-stationary event based on signal parameters sampled from a frame of the error signal comprises:
 applying a peak tracker and a valley tracker, using a voice activity detector, to a current frame of the error signal to determine the amplitude and number of peaks in the current frame; and 
 detecting a presence of speech when a predetermined number of peaks exceed a predetermined value over a predetermined duration. 
 
     
     
       7. The method of  claim 1 , wherein modifying an adaption parameter includes reducing a rate of adaptation of one or more controllable filters. 
     
     
       8. The method of  claim 1 , wherein modifying an adaption parameter includes pausing adaptation of one or more controllable filters by reducing a rate of adaptation of the controllable filters to zero. 
     
     
       9. The method of  claim 1 , wherein modifying an adaption parameter includes deactivating the EOC system for the duration of the frame. 
     
     
       10. An engine order cancellation (EOC) system comprising:
 a noise signal generator, having a frequency generator, adapted to generate a noise signal in response to an input; 
 a controllable filter adapted to generate an anti-noise signal based in part on an adaptive transfer characteristic, the anti-noise signal to be radiated by a speaker as anti-noise within a cabin of a vehicle; 
 an adaptive filter controller, including a processor and memory, programmed to control the adaptive transfer characteristic of the controllable filter based on the noise signal received from the noise signal generator, an error signal received from a microphone located in the cabin of the vehicle, and an adaptation parameter; and 
 a signal analysis controller, including a processor and memory, programmed to:
 detect a non-stationary event based on parameters sampled from a current frame of the error signal; and 
 modify at least one of the adaptation parameter and the error signal in response to detecting the non-stationary event. 
 
 
     
     
       11. The EOC system of  claim 10 , wherein the adaptation parameter determines a rate of change of the adaptive transfer characteristic for the controllable filter. 
     
     
       12. The EOC system of  claim 11 , wherein the signal analysis controller is programmed to modify the adaption parameter by reducing a rate of adaptation of the controllable filters. 
     
     
       13. The EOC system of  claim 10 , wherein the signal analysis controller is programmed to modify the error signal by removing non-stationary noise indicated by the non-stationary event to generate an adjusted error signal. 
     
     
       14. The EOC system of  claim 10 , further comprising a voice activity detector in communication with the signal analysis controller that detects speech present in the error signal, wherein the non-stationary event includes the speech. 
     
     
       15. The EOC system of  claim 14 , wherein the voice activity detector is configured to determine a zero-crossing rate in the current frame of the error signal. 
     
     
       16. The EOC system of  claim 10 , wherein the signal analysis controller is programmed to detect a non-stationary event based on parameters sampled from a current frame of the error signal by comparing at least one signal parameter of a current frame for each error signal to a threshold. 
     
     
       17. The EOC system of  claim 10 , wherein the noise signal generator further includes an RPM sensor and a lookup table. 
     
     
       18. A non-transitory computer readable medium storing instructions for engine order cancellation (EOC), the instructions comprising:
 one or more instructions that, when executed by one or more processors, cause the one or more processors to:
 receive noise signals from at least one noise signal generator; 
 generate an anti-noise signal to be radiated by a speaker as anti-noise within a cabin of a vehicle, the anti-noise signal being generated by at least one controllable filter based in part on the noise signals from the at least one noise signal generator; 
 receive error signals from at least one microphone located in the cabin of the vehicle; 
 detect a non-stationary event based on signal parameters sampled from a frame of at least one error signal; and 
 modify the anti-noise signal for the duration of the frame in response to detecting the non-stationary event. 
 
 
     
     
       19. The non-transitory computer readable medium of  claim 18 , wherein the one or more instructions, that cause the one or more processors to modify the anti-noise signal for the duration of the frame in response to detecting the non-stationary event, cause the one or more processors to:
 modify an adaptation parameter that controls a rate of adaptation of the controllable filter. 
 
     
     
       20. The non-transitory computer readable medium of  claim 18 , wherein the one or more instructions, that cause the one or more processors to modify the anti-noise signal for the duration of the frame in response to detecting the non-stationary event, cause the one or more processors to:
 modify the error signal by removing non-stationary noise indicative of the non-stationary event to obtain an adjusted error signal.